How to make outlined texture in blender?
I add this to show some example related to your edited question:

You say very little about your object mesh, but it seems you set a linestyle thickness quite high for the overall mesh size.

I try to replicate it here:



where you can see the corners are not that good but just changing one setting gets  better results:



of course you have to experiment, to find your best setting, and freestyle really has tons of settings...